Spring system for mems device

ABSTRACT

A spring system ( 74 ) links a pair of drive masses ( 30, 32 ) of a MEMS device ( 72 ). The spring system ( 74 ) includes stiff beams ( 76, 78, 80, 82 ) oriented to form a parallelogram arrangement ( 84 ). The beams are oriented diagonal to a drive direction ( 56 ) of the masses ( 30, 32 ). Diagonally opposing corners ( 86, 88 ) of the parallelogram arrangement ( 84 ) are coupled to the drive masses ( 30, 32 ). A spring ( 90 ) is coupled to a corner ( 94 ) and a spring ( 92 ) is coupled to a diagonally opposing corner ( 96 ) of the parallelogram arrangement. The springs ( 90, 92 ) are interconnected with a sense frame ( 34 ) surrounding the drive masses. The beams and side springs are stiff to substantially prevent in-phase motion ( 66 ) of the drive masses. However, rotationally compliant flexures ( 102, 104, 106, 108 ), allow the arrangement ( 84 ) to collapse and expand to enable anti-phase motion ( 60 ) of the drive masses.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to microelectromechanicalsystems (MEMS) devices. More specifically, the present invention relatesto a MEMS device that is insusceptible to in-phase motion.

BACKGROUND OF THE INVENTION

Microelectromechanical systems (MEMS) technology has achieved widepopularity in recent years, as it provides a way to make very smallmechanical structures and integrate these structures with electricaldevices on a single substrate using conventional batch semiconductorprocessing techniques. One common application of MEMS is the design andmanufacture of sensor devices. MEMS sensor devices are widely used inapplications such as automotive, inertial guidance systems, householdappliances, game devices, protection systems for a variety of devices,and many other industrial, scientific, and engineering systems. Oneexample of a MEMS sensor is a MEMS angular rate sensor. An angular ratesensor senses angular speed or velocity around one or more axes.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the detailed description and claims when considered inconnection with the Figures, wherein like reference numbers refer tosimilar items throughout the Figures, and:

FIG. 1 shows a top view of a prior art angular rate sensor;

FIG. 2 shows a conceptual model of the drive masses for the prior artangular rate sensor under two modes of operation;

FIG. 3 shows a top view of an angular rate sensor in accordance with anembodiment;

FIG. 4 shows a top view of a portion of the angular rate sensor of FIG.3;

FIG. 5 shows a conceptual model of drive masses for the angular ratesensor of FIG. 3 coupled via a spring system in accordance with anembodiment;

FIG. 6 shows the conceptual model of FIG. 5 demonstrating anti-phasemotion of the drive masses in a first direction; and

FIG. 7 shows the conceptual model of FIG. 5 demonstrating anti-phasemotion of the drive masses in a second direction.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, FIG. 1 shows a top view of a prior artangular rate sensor 20 and FIG. 2 shows a conceptual model 21 of thedrive masses for the prior art angular rate sensor 20 under two modes ofoperation. Prior art angular rate sensor 20 is provided herein toillustrate unwanted in-phase motion that may occur in prior art designs.Angular rate sensor 20 is generally configured to sense angular rateabout an axis of rotation referred to as an input axis 22. In theillustrated configuration, input axis 22 is the X-axis in athree-dimensional coordinate system. By convention, angular rate sensor20 is illustrated as having a generally planar structure within an X-Yplane 24, wherein a Z-axis 26 extends out of the page, normal to X-Yplane 24 in FIG. 1.

Angular rate sensor 20 includes a substrate 28, a drive mass 30, anotherdrive mass 32, a sense mass 34, and various mechanical linkages. In theexample of FIG. 1, sense mass 34 is a sense frame, and drive masses 30and 32 reside in a central opening 36 extending through sense mass 34.Drive mass 32 is disposed laterally in X-Y plane 24 from drive mass 30,and drive masses 30 and 32 are situated symmetrically relative to oneanother about input axis 22.

Link spring components 38 couple each of drive masses 30 and 32,respectively, to sense mass 34. As such, drive masses 30 and 32 aresuspended above a surface 40 of substrate 28 and do not have a directphysical attachment to substrate 28. Angular rate sensor 20 furtherincludes flexible support elements in the form of torsion springs 42coupled to sense mass 34. Torsion springs 42 connect sense mass 34 tosurface 40 of substrate 28 via anchors 44.

A variety of conductive plates, or electrodes, may be formed on surface40 of substrate 28 in conjunction with the other fixed components ofangular rate sensor 20. In this simplified illustration, the electrodesinclude sense electrodes 46 and 48, used to sense the rotation ofangular rate sensor 20 about X-axis 22. Electrodes 46 and 48 areobscured in FIG. 1 by the overlying sense mass 34. Accordingly, in FIG.1, electrodes 46 and 48 are represented in dashed line form toillustrate their physical placement relative to sense mass 34.

A drive system 50 resides in central opening 36. Drive system 50includes sets of drive elements configured to oscillate drive masses 30and 32. Each set of drive elements includes pairs of electrodes,referred to as movable fingers 52 and fixed fingers 54. In theillustrated example, movable fingers 52 are coupled to and extend fromeach of drive masses 30 and 32 and fixed fingers 54 are fixed to surface40 of substrate 28. Fixed fingers 54 are spaced apart from andpositioned in alternating arrangement with movable fingers 52. By virtueof their attachment to drive masses 30 and 32, movable fingers 52 aremovable together with drive masses 30 and 32. Conversely, due to theirfixed attachment to substrate 28, fixed fingers 54 are stationaryrelative to movable fingers 52.

Drive masses 30 and 32 may be configured to undergo oscillatory motionwithin X-Y plane 24. In general, an alternating current (AC) voltage, asa drive signal, may be applied to fixed fingers 54 via a drive circuit(not shown) to cause drive masses 30 and 32 to oscillate along a driveaxis 56, i.e., the Y-axis, in the three dimensional coordinate system.Drive masses 30 and 32 are linked together via a coupling spring 58 tomove in opposite directions, i.e., anti-phase, along Y-axis 56.

In operation, drive system 50 imparts oscillatory linear motion on drivemasses 30 and 32 within X-Y plane 24 in anti-phase. In the illustratedembodiment, wherein the axis of rotation is designated as X-axis 22,drive masses 30 and 32 oscillate in opposite directions approximatelyparallel to Y-axis 46 (i.e., up and down in FIG. 1). Anti-phase movementof drive masses 30 and 32 is represented in FIGS. 1 and 2 by oppositelypointing arrows 60, and is thus referred to herein as anti-phase motion60. Once drive masses 30 and 32 are put into oscillatory motion (i.e.,anti-phase motion 60) along Y-axis 46, the system of masses 30, 32, and34 is capable of detecting angular rate, i.e., angular velocity, inducedby angular rate sensor 20 being rotated about X-axis 22. In particular,as a result of a Coriolis acceleration component, torsion springs 42enable sense mass 34 to oscillate out of X-Y plane 24 by pivoting abouttorsion springs 42 as a function of angular rate, i.e., the angularvelocity, of angular rate sensor 20 about X-axis of rotation 22. Thismovement has an amplitude that is proportional to the angular rotationrate of angular rate sensor 20 about the input axis, i.e., X-axis 22,which is sensed at electrodes 46 and 48.

With particular reference to conceptual model 21 of FIG. 2, angular ratesensor 20 (FIG. 1) is represented by drive masses 30 and 32 linked bycoupling spring 58, and link spring components 38 that couple drivemasses 30 and 32 to sense mass 34. The system of springs 38 and 58enable anti-phase motion 60 of drive masses 30 and 32. An equation 62represents an anti-phase drive frequency component 64 for anti-phasemotion 60 imparted on drive masses 30 and 32.

Drive masses 30 and 32 can be subjected to in-phase movement due toexternal vibration, shock, interference, and the like. In-phase movementrefers to a condition in which the two drive masses 30 and 32 oscillatein the same direction at the same amplitude. In-phase movement of drivemasses 30 and 32 is represented in FIG. 2 by a pair of arrows 66pointing in the same direction, and is thus referred to herein asin-phase motion 66. In-phase motion 66 is disadvantageous in angularrate sensor 20. Indeed, external vibration at the resonant frequency ofthe undesired in-phase mode can produce significant in-phase motion 66thus causing uncontrollable large motion of drive masses 30 and 32leading to inaccuracy of an angular rate sensor. Unfortunately, thesystem of springs 38 and 58 in the exemplary prior art design may allowfor the undesired in-phase motion 66 of drive masses 30 and 32. Anequation 68 represents an in-phase frequency component 70 for in-phasemotion 66 imparted on drive masses 30 and 32.

Embodiments disclosed herein entail a spring system for amicroelectromechanical systems (MEMS) device, a MEMS device includingthe spring system, and a method of fabricating the MEMS device havingthe spring system. In particular, a MEMS angular rate sensor includes aspring system coupling a pair of drive masses that enables fundamental“tuning fork” anti-phase motion of the drive masses. The spring systemincludes a rectangular structure of diagonally oriented stiff beamscoupled to the drive masses. The spring system further includes sidesprings interconnected between the rectangular structure and asurrounding sense frame that are stiff in the direction of drive motion,but compliant in a direction orthogonal to the direction of the drivemotion. The diagonally arranged beams are linked to the side springswith rotationally compliant flexures. The resulting structure constrainsthe motion of the drive masses to anti-phase oscillation and providesstiff resistance to in-phase oscillation of the drive masses. Although aMEMS angular rate sensor is described herein, it should be understoodthat the spring system may be adapted for use in other MEMs devicesimplementing dual movable drive masses that are to be driven inanti-phase, and for which in-phase motion is to be suppressed.

Referring to FIGS. 3-4, FIG. 3 shows a top view of an angular ratesensor 72 in accordance with an embodiment, and FIG. 4 shows a top viewof a portion of angular rate sensor 72. Like angular rate sensor 20,angular rate sensor 72 is generally configured to sense angular rateabout an axis of rotation referred to as input axis 22, i.e. the X-axis,where drive axis 56 is the Y-axis, and sense axis 26 is the Z-axis. Manyof the components of angular rate sensor 72 are the same as for angularrate sensor 20. As such, the same references numbers will be utilizedfor the same elements and a description of their structure and functionwill not be repeated. However, in accordance with an embodiment,coupling spring 58 (FIG. 1) is replaced by a spring system 74. Springsystem 74 is configured to reduce in-phase motion 66 of drive masses 30and 32.

Spring system 74 includes a set of stiff beams, the set including afirst beam 76, a second beam 78, a third beam 80, and a fourth beam 82.Beams 76, 78, 80, and 82 are oriented diagonal to, i.e. slantedobliquely relative to, a drive direction of drive masses 30 and 32. Thatis, beams 76, 78, 80, and 82 are oriented diagonal to drive axis 56. Theterm “diagonal” used herein refers to a configuration in which each ofbeams 76, 78, 80, and 82 are not arranged parallel to the drivedirection of drive masses 30 and 32, and beams 76, 78, 80, and 82 arenot arranged perpendicular to the drive direction of drive masses 30 and32. Instead, beams 76, 78, 80, and 82 may be slanted obliquely, althoughthey are not limited to a forty-five degree slant relative to the drivedirection. The terms “first,” “second,” “third,” and so forth usedherein do not refer to an ordering or prioritization of elements withina countable series of elements. Rather, the terms “first,” “second,”“third,” and so forth are used to distinguish certain elements, orgroups of elements, from one another for clarity of discussion.

Beams 76, 78, 80, and 82 are oriented relative to one another to form aparallelogram arrangement 84. As such, first and fourth beams 76 and 82are generally equal in length and parallel to one another. Likewise,second and third beams 78 and 80 are generally equal in length andparallel to one another. The parallelogram arrangement 84 of beams 76,78, 80, and 82 includes four corners. A first corner 86 of parallelogramarrangement 84 is configured to couple to drive mass 30, and a secondcorner 88 of parallelogram arrangement 84 is configured to couple drivemass 32, where second corner 88 is diagonally opposite to first corner86.

Spring system 74 further includes a first side spring 90 and a secondside spring 92. First side spring 90 is coupled to a third corner 94 ofparallelogram 84, and second side spring 92 is coupled to a fourthcorner 96 of parallelogram 84, where fourth corner 96 is diagonallyopposite to third corner 94. Opposing ends 98 and 100 of each of firstand second side springs 90 and 92 interconnect with the frame structureof sense mass 34. In an embodiment, first and second side springs 90 and92, respectively, are stiff in a drive direction of drive masses 30 and32. That is, first and second side springs 90 and 92 are thin in theX-direction as compared to their length in the Y-direction. Accordingly,first and second side springs 90 and 92 are resistant to bending in adrive direction that is parallel to drive axis 56. However, first andsecond side springs 90 and 92 are compliant, i.e., are able to bend,flex, or otherwise deform, in another direction that is parallel to X-Yplane 24. Thus, first and second side springs 90 and 92 are compliant ina direction that is substantially parallel to X-axis 22. As such, firstand second side springs 90 and 92 do not allow motion in the drivedirection, parallel to drive axis 56. Rather, first and second sidesprings 90 and 92 allow motion in another direction that is parallel toX-axis 22. This compliance is particularly exemplified in FIG. 4.

Spring system 74 further includes a first flexure arrangement 102interconnecting first and second beams 76 and 78, respectively, ofparallelogram arrangement 84 at first corner 86. Likewise, a secondflexure arrangement 104 interconnects third and fourth beams 80 and 82,respectively, at second corner 88. A third flexure arrangement 106interconnects first beam 76 and third beam 80 at third corner 94. And, afourth flexure arrangement 108 interconnects second beam 78 and fourthbeam 82 at fourth corner 96. Each of flexure arrangements 102, 104, 106,and 108 is rotationally compliant about an axis that is substantiallyperpendicular to the planar surface 40 of substrate 28. That is, each offlexure arrangements 102, 104, 106, and 108 are formed from any suitablespring configuration that allows for rotation about Z-axis 26. However,flexure arrangements 102, 104, 106, and 108 are axially stiff, i.e., areprevented from linear movement parallel to Z-axis 26, so that therotational movement of flexure arrangements 102, 104, 106, 108 isconstrained to X-Y plane 24.

Additionally, the spring constants of beams 76, 78, 80, and 82 can betuned to be much stiffer than that of flexure arrangements 102, 104,106, 108 so that beams 76, 78, 80, and 82 are largely non-compliant andflexure arrangements are more compliant than 76, 78, 80, and 82. Forexample, the width of beams 76, 78, 80, and 82 in X-Y plane 24 may besignificantly greater than the width of any of flexure arrangements 102,104, 106, and 108 in X-Y plane.

FIG. 5 shows a conceptual model 110 of drive masses 30, 32 for angularrate sensor 72 (FIG. 3) coupled via spring system 74 in accordance withan embodiment. In conceptual model 110, first and second side springs 90and 92 are each represented by an element 112 and a spring 114. Asdescribed above, first and second side springs 90 and 92 (represented byelement 112 and spring 114) interconnect parallelogram arrangement 84 ofstiff beams 76, 78, 80, and 82 with sense frame 34.

As discussed previously, first and second side springs 90 and 92 arestiff, i.e., non-compliant, in the Y-direction parallel to Y-axis 56.This stiffness is represented in conceptual model 110, by element 112being constrained by fixed structures 116. However, spring 114represents the ability of each of first and second side springs 90 and92 to move, i.e., stretch, compress, or otherwise deform, in a directionparallel to X-axis 22.

The stiffness of beams 76, 78, 80, and 82, as well as the stiffness offirst and second side springs 90 and 92 in the Y-direction, providemechanical constraint to in-phase motion 66 at the resonant frequency,i.e., the operating frequency, of angular rate sensor 72. Thus, in-phasemotion 66 of drive masses 30 and 32 due to external vibration, spuriousacceleration, or interference is largely prevented. The mechanicalconstraint of spring system 74 can push the in-phase frequency component70 (FIG. 2) due to in-phase motion 66 sufficiently high so that in-phasefrequency component 70 is outside of the operating range of angular ratesensor 72.

Referring to FIGS. 6 and 7, FIG. 6 shows conceptual model 110demonstrating anti-phase motion 60 of drive masses 30 and 32 in a firstdirection 118, and FIG. 7 shows conceptual model 110 demonstratinganti-phase motion 60 of drive masses 30 and 32 in a second direction120. Drive masses 30 and 32 are driven into anti-phase motion 60 viadrive system 50, as discussed above in connection with FIG. 1.

In FIG. 6, a drive signal from drive system 50 moves drive masses 30 and32 in first direction 118 toward one another. As drive masses 30 aredriven toward one another, flexure arrangements 102, 104, 106, and 108enable rotational movement of beams 76, 78, 80, and 82, as representedby arrows 122, so that side springs 90 and 92 deform in the X-directionand parallelogram arrangement 84 collapses, i.e., compresses, in thedrive direction. In FIG. 7, the drive signal from drive system 50 movesdrive masses 30 and 32 in second direction 120 away from one another. Asdrive masses 30 are driven away from one another, flexure arrangements102, 104, 106, and 108 again enable rotational movement 122 of beams 76,78, 80, and 82, so that side springs 90 and 92 deform in the X-directionand parallelogram arrangement 84 expands in the drive direction. Thus,oscillatory anti-phase motion 60 of first and second drive masses 30 and32 is enabled, while in-phase motion 66 (FIG. 5) is substantiallyprevented. Furthermore, parallelogram arrangement 84 is constrained to anon-collapsed configuration 124 (FIG. 5) when subjected to an externalvibration due to the non-compliance of first and second side springs 90and 92 in the Y-direction.

Referring back to FIG. 3, a method of fabricating angular rate sensor 72generally entails forming first drive mass 30, second drive mass 32, andsense mass 34 surrounding drive masses 30 and 32 suspended above surface40 of substrate 28. Spring system 74 is formed to include the set ofstiff (e.g., relatively thick in X-Y plane 24) beams 76, 78, 80, and 82oriented relative to one another to form parallelogram structure 84, andformed to include first and second side springs 90 and 92, respectively.The fabrication of angular rate sensor 72 results in spring system 74being coupled to drive masses 30 and 32 such that beams 76, 78, 80, and82 are oriented diagonal to drive direction 56 of drive masses 30 and32. The fabrication of angular rate sensor 72 further results in firstcorner 86 of parallelogram arrangement 84 being interconnected withfirst drive mass 30 and second corner 88 of parallelogram arrangement 84being interconnected with second drive mass 32, where second corner 88is diagonally opposite said first corner. The fabrication of angularrate sensor 72 further also results in first side spring 90 beinginterconnected with third corner 94 of parallelogram arrangement 84 andsecond side spring 92 being interconnected with fourth corner 96 ofparallelogram arrangement 84, where fourth corner 96 is diagonallyopposite third corner 94. Additionally, the interconnection of suitableflexure arrangements 102, 104, 106, and 108 occurs, and theinterconnection of opposing ends 98 and 100 of side springs 90 and 92 tosense mass 34 occurs during fabrication.

Fabrication of angular rate sensor 72 may be performed using anysuitable known or upcoming fabrication process. For example, afabrication process implements a silicon micromachining fabricationprocess that results in structural layers and sacrificial layers thatare appropriately deposited, patterned, and etched to produce thesuspended structures of angular rate sensor 72.

In summary, embodiments entail a spring system for amicroelectromechanical systems (MEMS) device, a MEMS device includingthe spring system, and a method of fabricating the MEMS device havingthe spring system. In particular, a MEMS angular rate sensor includes aspring system coupling a pair of drive masses that enables fundamentalanti-phase motion of the drive masses. The spring system includes aparallelogram arrangement of diagonally oriented stiff beams coupled tothe drive masses. The spring system further includes side springsinterconnected between the parallelogram arrangement and a surroundingsense frame that are stiff in the direction of drive motion, butcompliant in a direction orthogonal to the direction of the drivemotion. The diagonally arranged beams are linked to the side springswith rotationally compliant flexures. The resulting structure constrainsthe motion of the drive masses to anti-phase oscillation and providesstiff resistance to in-phase oscillation of the drive masses.Consequently, greater accuracy of the signal output can be achieved.

Although the preferred embodiments of the invention have beenillustrated and described in detail, it will be readily apparent tothose skilled in the art that various modifications may be made thereinwithout departing from the spirit of the invention or from the scope ofthe appended claims. That is, it should be appreciated that theexemplary embodiments are only examples, and are not intended to limitthe scope, applicability, or configuration of the invention.

What is claimed is:
 1. A microelectromechanical systems (MEMS) devicecomprising: a first movable mass; a second movable mass; and a springsystem for coupling said first movable mass to said second movable mass,said spring system comprising: a set of stiff beams oriented relative toone another to form a parallelogram arrangement, said beams beingoriented diagonal to a drive direction of said first and second movablemasses, wherein a first corner of said parallelogram arrangement isconfigured to couple to said first movable mass and a second corner ofsaid parallelogram arrangement is configured to couple to said secondmovable mass, said second corner being diagonally opposite said firstcorner; a first side spring coupled to a third corner of saidparallelogram arrangement; and a second side spring coupled to a fourthcorner of said parallelogram arrangement, said fourth corner beingdiagonally opposite said third corner.
 2. A MEMS device as claimed inclaim 1 wherein said spring system further comprises: a first flexurearrangement interconnecting a first beam and a second beam of saidparallelogram arrangement at said first corner; a second flexurearrangement interconnecting a third beam and a fourth beam of saidparallelogram arrangement at said second corner; a third flexurearrangement interconnecting said first beam and said third beam of saidparallelogram arrangement at said third corner; and a fourth flexurearrangement interconnecting said second beam and said fourth beam ofsaid parallelogram arrangement at said fourth corner, wherein each ofsaid first, second, third, and fourth flexure arrangements isrotationally compliant about an axis that is substantially perpendicularto a planar substrate of said MEMS device.
 3. A MEMS device as claimedin claim 2 wherein said each of said first, second, third, and fourthflexure arrangements is axially stiff to substantially limit rotationalmovement of said first, second, third, and fourth flexure arrangementsto a plane that is substantially parallel to said planar substrate.
 4. AMEMS device as claimed in claim 1 wherein said parallelogram arrangementis configured to collapse when subjected to a drive signal to enableanti-phase motion of said first and second movable masses.
 5. A MEMSdevice as claimed in claim 1 wherein said parallelogram arrangement isconstrained to a non-collapsed configuration when subjected to anexternal vibration signal.
 6. A MEMS device as claimed in claim 1wherein said first and second side springs are stiff in said drivedirection and compliant in a second direction that is orthogonal to saiddrive direction.
 7. A MEMS device as claimed in claim 6 wherein saiddrive direction and said second direction are substantially parallel toa planar substrate of said MEMS device.
 8. A MEMS device as claimed inclaim 1 further comprising a frame surrounding said first and secondmovable masses, wherein opposing ends of each of said first and secondside springs are adapted to interconnect with said frame.
 9. A MEMSdevice as claimed in claim 1 further comprising a planar substrate,wherein said set of stiff beams, said first side spring, and said secondside spring are suspended above said planar substrate without a directconnection to said planar substrate.
 10. A method of fabricating amicroelectromechanical systems (MEMS) device comprising: forming a firstmovable mass, a second movable mass, and a sense frame surrounding saidfirst and second movable masses on a planar substrate; forming a springsystem, said spring system including a set of stiff beams orientedrelative to one another to form a parallelogram arrangement, a firstside spring, and a second side spring; and wherein said spring system iscoupled to said first and second movable masses such that said beams areoriented diagonal to a drive direction of said first and second movablemasses, wherein a first corner of said parallelogram arrangement iscoupled to said first movable mass, a second corner of saidparallelogram arrangement is coupled to said second movable mass, saidsecond corner being diagonally opposite said first corner, and whereinsaid first side spring is coupled to a third corner of saidparallelogram arrangement, said second side spring is coupled to afourth corner of said parallelogram arrangement, said fourth cornerbeing diagonally opposite said third corner.
 11. A method as claimed inclaim 10 wherein following said forming operations: a first beam and asecond beam of said parallelogram arrangement are interconnected at saidfirst corner via a first flexure arrangement; a third beam and a fourthbeam of said parallelogram arrangement are interconnected at said secondcorner via a second flexure arrangement; said first beam and said thirdbeam of said parallelogram arrangement are interconnected at said thirdcorner via a third flexure arrangement; and said second beam and saidfourth beam of said parallelogram arrangement are interconnected at saidfourth corner via a fourth flexure arrangement, wherein each of saidfirst, second, third, and fourth flexure arrangements is rotationallycompliant about an axis that is substantially perpendicular to a planarsubstrate of said MEMS device.
 12. A method as claimed in claim 10wherein following said forming operations, opposing ends of each of saidfirst and second side springs are interconnected to said sense frame.13. A method as claimed in claim 10 wherein following said formingoperations, said parallelogram arrangement is configured to collapsewhen subjected to a drive signal to enable anti-phase motion of saidfirst and second movable masses, and said parallelogram arrangement isconstrained to a non-collapsed configuration when subjected to anexternal vibration signal.
 14. A method as claimed in claim 10 whereinsaid first and second side springs are stiff in said drive direction andcompliant in a second direction that is orthogonal to said drivedirection, said drive direction and said second direction beingsubstantially parallel to a planar substrate of said MEMS device.
 15. Amethod as claimed in claim 10 further comprising suspending saidparallelogram arrangement, said first side spring, and said secondspring above a planar substrate of said MEMS device without a directconnection to said planar substrate.
 16. A microelectromechanicalsystems (MEMS) device comprising: a substrate having a planar surface; asense frame suspended above and movably anchored to said planar surface,said sense frame having a central opening; a first drive mass; a seconddrive mass, said first and second drive masses being positioned withinsaid central opening of said sense frame; and a spring system configuredto reduce in-phase motion of said first and second movable masses, saidspring system including: a set of stiff beams oriented relative to oneanother to form a parallelogram arrangement, said beams being orienteddiagonal to a drive direction of said first and second movable masses, afirst corner of said parallelogram arrangement being coupled to saidfirst movable mass and a second corner of said parallelogram arrangementbeing coupled to said second movable mass, said second corner beingdiagonally opposite said first corner; a first side spring coupled to athird corner of said parallelogram arrangement, and having firstopposing ends interconnected with said sense frame; and a second sidespring coupled to a fourth corner of said parallelogram arrangement, andhaving second opposing ends interconnected with said sense frame, saidfourth corner being diagonally opposite said third corner, said firstand second side springs being stiff in said drive direction andcompliant in a second direction that is orthogonal to said drivedirection.
 17. A MEMS device as claimed in claim 16 wherein said springsystem further comprises: a first flexure arrangement interconnecting afirst beam and a second beam of said parallelogram arrangement at saidfirst corner; a second flexure arrangement interconnecting a third beamand a fourth beam of said parallelogram arrangement at said secondcorner; a third flexure arrangement interconnecting said first beam andsaid third beam of said parallelogram arrangement at said third corner;and a fourth flexure arrangement interconnecting said second beam andsaid fourth beam of said parallelogram arrangement at said fourthcorner, wherein each of said first, second, third, and fourth flexurearrangements is rotationally compliant about an axis that issubstantially perpendicular to said planar surface of said substrate.18. A MEMS device as claimed in claim 17 wherein said each of saidfirst, second, third, and fourth flexure arrangements is axially stiffto substantially limit rotational movement about said axis to a planethat is substantially parallel to said planar surface of said substrate.19. A MEMS device as claimed in claim 16 wherein said parallelogramarrangement is configured to collapse when subjected to a drive signalto enable anti-phase motion of said first and second movable masses, andsaid parallelogram arrangement is constrained to a non-collapsedconfiguration when subjected to an external vibration signal.
 20. A MEMSdevice as claimed in claim 16 wherein said drive direction and saidsecond direction are substantially parallel to said planar surface ofsaid substrate.